The interpretation of XUV rocket measurements of intensity ratios of solar spectral lines of the lithiumlike ions O vi,Ne viii,and Mg x     

L. Heroux  M. Cohen  Monique Malinovsky 《Solar physics》1972,23(2):369-393

A rocket borne spectrometer was flown to measure absolute intensities of extreme ultraviolet spectral lines from the three ions O vi, Ne viii, and Mg x present in the Sun. From these measurements, intensity ratios of lines from O vi, ratios of lines from Ne viii, and ratios of lines from Mg x were formed. These experimental ratios were compared with ratios calculated by using specific theoretical values of the ionization equilibrium in which dielectronic recombination was included in the processes establishing ionization balance. The effects of the electron density and temperature gradient on the temperature distribution of the flux of the spectral lines in the solar atmosphere have been taken into account in the calculations of the ratios. The agreement between the experimental and calculated ratios is good for the ions Ne viii and Mg x and satisfactory for the ion O vi for which the calculated ratio is subject to large uncertainties. A reliable measurement of the electron temperature in the lower corona was obtained from the experimental ratios for Mg x. This experimental temperature is in good agreement with the emission temperature of the spectral lines of Mg x predicted from the theoretical values of the ionization equilibrium. The design and photometric calibration of a new rocket spectrometer developed to measure the intensity ratios over the broad spectral region 50 to 1250 Å are also described.  相似文献   

Large‐eddy simulation of small‐scale surface effects on the convective boundary‐layer structure     

Shaohua Shen  Monique Y. Leclerc 《大气与海洋》2013,51(4):717-731

Abstract

The effects of small‐scale surface inhomogeneities on the turbulence structure in the convective boundary layer are investigated using a high‐resolution large‐eddy simulation model. Surface heat flux variations are sinusoidal and two‐dimensional, dividing the total domain into a checkerboard‐like pattern of surface hot spots with a 500‐m wavelength in the x and y directions, or 1/4 of the domain size. The selected wind speeds were 1 and 4 m s^‐l, respectively. As a comparison, a simulation of the turbulence structure was performed over a homogeneous surface.

When the wind speed is light, surface heat flux variations influence the horizontally averaged turbulence statistics, including the higher moments despite the small characteristic length of the surface perturbation. Stronger mean wind speeds weaken the effects of inhomogeneous surface conditions on the turbulence structure in the convective boundary layer.

Results from conditional sampling show that when the mean wind speed is small, weak mean circulations occur, with updraft branches above the high heat flux regions and down‐draft branches above the low heat flux regions. The inhomogeneous surface induces significant differences in the turbulence statistics between the high and low heat flux regions. However, the effect of the surface perturbations weaken rapidly when the mean wind speed increases. This research has implications in the explanation of the large‐scale variability commonly encountered in aircraft observations of atmospheric turbulence.  相似文献   

Risk of injury and death from lightning in Northern Malawi     

Jonathan Salerno  Lameck Msalu  Tim Caro  Monique Borgerhoff Mulder 《Natural Hazards》2012,62(3):853-862

Rates of lightning mortality in communities on the western shore of Lake Malawi are higher than any other reported rate in the world: 419 strike victims per million people per annum and 84 deaths per million per annum. To document the background to this phenomenon, we conducted comprehensive household interviews with surviving victims and witnesses of every case of lightning strike in seven administrative areas around Nkhata Bay, Malawi. We find that the consequential lightning strikes are significantly more common in the rainy season and during the morning. Among those victims struck by lightning, there is an average ratio of approximately one death to four injuries, which is substantially higher than the commonly accepted ratio of 1:10. Children and adults are at equal risk of being struck. If struck, the probability of death is greater when the victim is outside in the open or outside under cover than indoors under a tin or thatched roof, but is unaffected by different kinds of footwear or whether it is raining. Reported explanations for strikes often center on witchcraft or other forms of social conflict. Our findings extend the study of consequential lightning strikes in the developing world and highlight cultural factors associated with this hazard. We end with recommendations for reducing the risk of lightning for rural populations.  相似文献   

Quantifying large‐scale historical formation of accommodation in the Mississippi Delta     

Robert A. Morton  Julie C. Bernier  Kyle W. Kelso  John A. Barras 《地球表面变化过程与地形》2010,35(14):1625-1641

Large volumes of new accommodation have formed within the Mississippi Delta plain since the mid‐1950s in association with rapid conversion of coastal wetlands to open water. The three‐dimensional aspects and processes responsible for accommodation formation were quantified by comparing surface elevations, water depths, and vertical displacements of stratigraphic contacts that were correlated between short sediment cores. Integration of data from remotely sensed images, sediment cores, and water‐depth surveys at 10 geologically diverse areas in the delta plain provided a basis for estimating the total volume of accommodation formed by interior‐wetland subsidence and subsequent erosion. Results indicate that at most of the study areas subsidence was a greater contributor than erosion to the formation of accommodation associated with wetland loss. Tens of millions of cubic meters of accommodation formed rapidly at each of the large open‐water bodies that were formerly continuous interior delta‐plain marsh. Together the individual study areas account for more than 440 × 10⁶ × m³ of new accommodation that formed as holes in the Mississippi River delta‐plain fabric between 1956 and 2004. This large volume provides an estimate of the new sediment that would be needed just at the study areas to restore the delta‐plain wetlands to their pre‐1956 areal extent and elevations. Published 2010. This article is a US Government work and is in the public domain in the USA.  相似文献   

Assimilation and High Resolution Forecasts of Surface and Near Surface Conditions for the 2010 Vancouver Winter Olympic and Paralympic Games     

Natacha B. Bernier  Stéphane Bélair  Bernard Bilodeau  Linying Tong 《Pure and Applied Geophysics》2014,171(1-2):243-256

A dynamical model was experimentally implemented to provide high resolution forecasts at points of interests in the 2010 Vancouver Olympics and Paralympics Region. In a first experiment, GEM-Surf, the near surface and land surface modeling system, is driven by operational atmospheric forecasts and used to refine the surface forecasts according to local surface conditions such as elevation and vegetation type. In this simple form, temperature and snow depth forecasts are improved mainly as a result of the better representation of real elevation. In a second experiment, screen level observations and operational atmospheric forecasts are blended to drive a continuous cycle of near surface and land surface hindcasts. Hindcasts of the previous day conditions are then regarded as today’s optimized initial conditions. Hence, in this experiment, given observations are available, observation driven hindcasts continuously ensure that daily forecasts are issued from improved initial conditions. GEM-Surf forecasts obtained from improved short-range hindcasts produced using these better conditions result in improved snow depth forecasts. In a third experiment, assimilation of snow depth data is applied to further optimize GEM-Surf’s initial conditions, in addition to the use of blended observations and forecasts for forcing. Results show that snow depth and summer temperature forecasts are further improved by the addition of snow depth data assimilation.  相似文献   

New insights into the age and formation of the Ankarokaroka lavaka and its associated sandy cover (NW Madagascar,Ankarafantsika natural reserve)          下载免费PDF全文

Michel Mietton  Stéphane Cordier  Manfred Frechen  Michel Dubar  Monique Beiner  Rafolo Andrianaivoarivony 《地球表面变化过程与地形》2014,39(11):1467-1477

Lavaka represent a typical erosional landform in Madagascar. The chronology of their formation remains, however, under discussion. Our research focuses on the Ankarokaroka lavaka, a spectacular landform located in NW Madagascar (Ankarafantsika natural reserve), which is characterized by the presence of sandy units of regional extension at its top. The two main units correspond to white and red sands, and are closely associated with specific vegetations (dry dense forest for the white sands, savannah grasslands for the red sands). We applied a geochronological approach based on Optically Stimulated Luminescence (for the coversands) associated with radiocarbon dating performed on archaeological remains found at the contact between the sands and the lavaka. The combination of this approach with field work and sedimentological analyses makes it possible to show that the sands experienced a complex history, both in terms of sedimentation and post‐sedimentary pedogenesis (podzolization of the white sands, rubefaction of the red sands). The numerical ages furthermore indicate that the Ankarokaroka lavaka formed between 18.5 ± 2.3 ka ago and the 14th century AD. The present study demonstrates that this lavaka has a climatic origin, and highlights the potential of OSL to date sediments associated with Madagascar lavaka. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Influence of Nocturnal Low-level Jets on Eddy-covariance Fluxes over a Tall Forest Canopy     

Thara V. Prabha  Monique Y. Leclerc  Anandakumar Karipot  David Y. Hollinger  Erich Mursch-Radlgruber 《Boundary-Layer Meteorology》2008,126(2):219-236

Observations of low-level jets (LLJs) at the Howland AmeriFlux site in the USA and the jet’s impact on nocturnal turbulent exchange and scalar fluxes over a tall forest canopy are discussed. Low-frequency motions and turbulent bursts characterize moderately strong LLJs, whereas low-frequency motions are suppressed during periods with strong LLJs and enhanced shear. An analysis based on the shear-sheltering hypothesis seeks to elucidate the effect of LLJs on flux measurements. In the absence of shear sheltering, large eddies penetrate the roughness sublayer causing enhanced mixing while during periods with shear sheltering, mixing is reduced. In the absence of the latter, ‘upside-down’ eddies are primarily responsible for the enhanced velocity variances, scalar and momentum fluxes. The integral length scales over the canopy are greater than the canopy height. The variance spectra and cospectra from the wavelet analysis indicate that large eddies (spatial scale greater than the low-level jet height) interact with active canopy-scale turbulence, contributing to counter-gradient scalar fluxes.  相似文献   

Regimes of spatial ordering in Brazil: Neoliberalism,leftist populism and modernist aesthetics in slum upgrading in Recife     

Monique Nuijten  Martijn Koster  Pieter de Vries 《Singapore journal of tropical geography》2012,33(2):157-170

This paper shows how regimes of spatial ordering in Brazil are produced by the entangling of neoliberalism, leftist populism and modernist visions. The paper focuses on Prometrópole, a slum upgrading project in Recife funded by the World Bank, which commenced in 2007. In this project, the neoliberal dimension manifests in the idea that the state, private companies and citizens together are responsible for (re)constructing urban space, and further, that beneficiaries should behave as autonomous citizens, taking responsibility for their new living environment. The leftist political dimension is seen in participatory procedures to involve the target population from project design through to implementation, in expectation of their cooperation with the government. The modernist aesthetics – of straight lines, open spaces and visible order – informs the project design with the requirement to use the new houses and public spaces according to the standards of ‘modern civilization’. As our research shows, such a regime of spatial ordering clashes with the livelihoods of the urban poor, whose quality of life might even deteriorate as a result of the intervention. Furthermore, so‐called participatory procedures fail to grant the target population any real influence in creating their environment. Consequently, these residents of the new housing estate drastically reconstruct their private and public areas, reappropriating the urban space and contesting the regime of spatial ordering imposed upon them.  相似文献   

Assessing the shear-sheltering theory applied to low-level jets in the nocturnal stable boundary layer   总被引：1，自引：0，他引：1  

Henrique F. Duarte  Monique Y. Leclerc  Gengsheng Zhang 《Theoretical and Applied Climatology》2012,110(3):359-371

This paper investigates the existence of shear sheltering on turbulence data over a quasi-ideal experimental site in Oklahoma, USA. Originally developed for engineering flows, the shear-sheltering theory is predicated upon the idea of low-level jets blocking large eddies aloft, preventing them from propagating to the surface. In this scenario, suppression of low-frequency turbulence energy and reduction of surface fluxes would be expected. Results from the Oklahoma experiment show instead an enhancement of surface turbulence intensity and of the relative contribution of large scales to total (co)variances for low-level jet cases with strong shear, thus suggesting the absence of shear sheltering at the site. The results underline the complexity of surface-atmosphere interactions in nocturnal stable conditions. Atmospheric modeling of exchange using various scenarios of surface characteristics, flow regimes, and low-level jet properties is suggested to further assess the potential applicability of the shear-sheltering theory to atmospheric flows.  相似文献   

Extreme sea levels,coastal flooding and climate change with a focus on Atlantic Canada     

Keith R. Thompson  Natacha B. Bernier  Paul Chan 《Natural Hazards》2009,51(1):139-150

Estimation of the probability distribution of extreme sea levels, for the present time and the next century, is discussed. Two approaches are described and their strengths and weaknesses are compared. The first approach is based on dynamics and uses a storm surge model forced by tides, winds and air pressure fields. The second approach is based on the statistical analysis of observed hourly sea level records using a new first-order Markov process that can capture non-Gaussian characteristics (such as skewness) in the non-tidal component of the observed sea level record. It is shown that both approaches can provide good estimates of present day flooding probabilities for regions with relatively strong tides. The limitations of both approaches in terms of assessing the effect of global sea level rise, glacial-isostatic adjustment of the land, and changes in the frequency and severity of storms and hurricanes, are illustrated using recent results for the Northwest Atlantic. Some sensitivity studies are carried out to transform uncertainty in climate change projections into uncertainties in the probability of coastal flooding.  相似文献